1. Field of the Invention
The present invention relates to a pulse detonation engine for possible application as a propulsion engine for a spaceplane, high-speed aircraft, or launch rocket and the like, and more particularly to a pulse detonation ramjet engine suitable as an engine required for operation at flight speeds from takeoff to hypersonic, and a valve employed therein.
2. Description of the Related Art
The detonation phenomenon is a supersonic combustion phenomenon accompanied by a vertical shockwave at the front face of the combustion wave, and has a greater produced energy density than normal subsonic combustion (deflagnation), and generates a combustion gas of higher temperature and pressure. Research into the control and effective use of this [detonation phenomenon] has been conducted (see Popular Science Magazine, November 2003 “Detonation—The Battle for the Next Generation Engine”, and AIAA-95-2577 “A Rotary Valve Multiple Pulse Detonation Engine (RVMPDE)) in recent years in association with clarification of detonation wave cell structures and transition conditions and timing and the like for deflagnation detonation. The pulse detonation engine is an engine where detonation is employed in the combustion process, and, as shown schematically in FIGS. 5A through 5C, is an intermittent combustion engine where a gaseous mixture of fuel and oxidizer is repeatedly introduced into, combusted in, and exhausted from, a combustor (combustion tube) 31 at a frequency of between 10 Hz and 100 Hz. In the process of filling the gaseous mixture, the gaseous mixture is supplied into the combustor 31, ignited at the closed end 32 of the combustor, and the combustion wave transformed from a deflagnation wave to a detonation wave during propagation from the closed end to the open end 33. Once a detonation wave 35 is formed, the high temperature and high-pressure combustion gas generated by combustion generates a large thrust at the closed end 32. When the detonation wave 35 reaches the open end 33 and the exhaust process commences, combustion gas is exhausted until the pressure of the open end 33 is equal with the external air pressure.
As an example of a pulse detonation engine employing such a detonation phenomenon, an engine combining a turbofan jet engine with a pulse detonation engine has been proposed (see Japanese Patent Application Laid-open No. 2001-355515) as a pulse detonation engine operating over a wide range of flight speeds. Furthermore, since the pulse detonation engine is, as described above, an intermittent combustion engine, in order to generate thrust continuously with sequential operation in an effective cycle using a plurality of combustors, combustor inlet valves supplying and controlling the gaseous mixture to the combustors are required to open and close rapidly with precise timing. A pulse detonation engine provided with a rotary disk valve has been proposed to satisfy this requirement (see for example, U.S. Pat. No. 5,353,588, and U.S. Pat. No. 5,473,885).
Previously proposed pulse detonation engines provide an opening and closing valve in the combustor inlet for supply and control of the gaseous mixture to permit the cycle of filling with the gaseous mixture, its combustion and exhaust, however the outlet of the combustor communicates directly with the nozzle and is always open to atmosphere. Thus, since the combustor is not isolated from the external atmosphere in the gaseous mixture filling process, the filling pressure and density are slightly greater than that of the external air. Thrust density of the combustor (=produced thrust÷combustor cross-sectional area) is therefore restricted by external air pressure, and is reduced as flight altitude increases. For this reason, pulse detonation engines are considered unsuitable as supersonic air-breathing engines at high altitude, and the advantages of high specific impulse are not obtained. Furthermore, since pulse detonation engines repeat combustion rapidly as described above, rapid opening and closing of the inlet valve supplying the gaseous mixture to the combustor is required, and they are subject to the problem of ready fatigue break due to vibration and repetitive stress resulting from combustion.